We propose to extensively characterize the process and consequences of down-regulation of Prostaglandin E1 (PGE) binding sites in liver plasma membranes. Changes in PGE binding site number and affinity will be related to changes in basal and stimulated (by PGE1, PGE2, glucagon and sodium fluoride) adenylate cyclase activity. Both the PGE binding studies and the adenylate cyclase experiments will be conducted in the presence and absence of GTP. Initially, we will extend our on-going studies of receptor down-regulation in vivo in rats by treatment with an analog of PGE2 (16,16-dimethyl PGE2). We will establish the dose-response curve for this analog and the duration of time required for down-regulation by the analog. Next, studies of receptor up-regulation will be performed using indomethacin and acetyl salicylic acid (PGE synthesis inhibitors), again assessing dose-response effects and the influence of time of drug exposure on these effects. Concurrently, we will chemically and physiologically characterize plasma membrane receptors for PGE coupled with adenylate cyclase in normal rabbits. This will be a necessary control set of experiments for subsequent studies using the VX2 tumor-bearing rabbit model. The VX2 tumor is readily transplanted into rabbits where it synthesizes and releases PGE2 production. This model will allow us to test the physiologic relevance of our experiments using the exogenous PGE2 analog in rats and rabbits. Throughout all of these studies, immunoassays for PGE2 and 13,14-dihydro-15-keto-PGE2 (the major circulating metabolite) and a receptor assay for the PGE2 analog will be used to determine, respectively, the degree of PGE synthesis inhibition by acetylsalicylic acid and indomethacin and the levels of the analog in samples of plasma and liver tissue. These measurements will be related to the changes in PGE binding site regulation and consequent changes in adenylate cyclase stimulation. These studies should increase our understanding of PGE receptor regulation in the liver which should in turn assist us in attaining our long term goal of understanding what role liver glycogenolysis plays in PGE2-induced hyperglycemia.